The present invention generally relates to printers, and more particularly to a drive system for use with a printing head (i.e., inkjet head) in an inkjet printer. The head drive system of the present invention is applicable not only to a single printer unit but also to an inkjet head which is widely usable for those copy machines, facsimile machines, computer systems and word processors, and combination machines thereof which have a printing function.
Among inkjet heads those which employ a piezoelectric element have increasingly come into the limelight in recent years due to its excellency in energy efficiency. This type of inkjet head generally includes a piezoelectric element, one common ink chamber which receives from an external device and stores ink, a plurality of pressure chambers coupled to the piezoelectric element, and a nozzle plate so connected to the pressure chambers that one nozzle may be connected to each pressure chamber. Each pressure chamber is connected to the common ink chamber through an ink introduction channel so that it may receive ink from the common ink chamber and increase its internal pressure using deformation of the piezoelectric element, thereby jetting ink from each nozzle. As a consequence, the inkjet head prints characters and images on a recording medium such as a printing paper.
One piezoelectric clement may be allocated to each pressure chamber (i.e., each nozzle), or may be allocated to all the pressure chambers while each pressure chamber is assigned to each of piezoelectric blocks as a divided piece in the piezoelectric element. A piezoelectric element or piezoelectric block (hereinafter simply called xe2x80x9cpiezoelectric elementxe2x80x9d) allocated to each pressure chamber may deform independently of those assigned to other pressure chambers, and thus each nozzle can jet ink independently of other nozzles.
Each piezoelectric element is typically comprised of a capacitive load containing a capacitor. Conventionally these piezoelectric elements have been connected commonly to and driven by a single drive control part. While the drive control part serves to generate and amplify a drive waveform, its amplifier part includes a bulk-size and large-capacitance transistor that requires high drive voltage and current so as to allow all the piezoelectric elements to drive simultaneously. The drive waveform determines a deformation amount of each piezoelectric element, and thus the drive circuit will in the event decide an ink-drop jet amount and speed, and ultimately the image quality.
A conventional inkjet printer has a disadvantage in that the drive control part often generates a distortional drive waveform and cannot provide high quality images. The recent demand for high-resolution images has more and more increased the number of nozzles and piezoelectric elements in an inkjet head, but this inventor has discovered that the distortional drive waveform accounts for the increased number of piezoelectric elements to be simultaneously driven.
A piezoelectric element as a capacitive load exposes itself to a sudden voltage chance and a large charge current especially at the time of ink jetting. This sudden change brings about distortion, and deteriorates the image quality as the number of piezoelectric elements increases. In addition, a push-pull circuit in the amplifier part in the drive control part when connected to a capacitive load is apt to oscillate. A push-pull circuit, which includes a pair of PNP and NPN transistors for use with power amplifications and impedance conversions, makes difficult such a circuit design of the amplifier part that operates stably for all combinations of driven piezoelectric elements. Oscillation in the push-pull circuit would distort a drive waveform and print undesired images. Moreover, a flexible cable which is connected to the drive control part and the head needs to flow a high-current and high-voltage drive waveform over a long distance, and its resistance and inductance components cause a voltage drop and distortion in the drive waveform.
On the other hand, a piezoelectric element has become more and more miniaturized, and drive voltage and current for driving each piezoelectric element have become reduced. Even a practical application is less likely to require all the piezoelectric elements to drive at the same time. Therefore, the present inventor has found that the conventional structure is uneconomical using a bulk transistor to drive a small number of piezoelectric elements.
Therefore, it is an exemplified general object of the present invention to provide a novel and useful inkjet head and its manufacturing method in which the above disadvantages are eliminated.
Another exemplified and more specific object of the present invention is to provide an inkjet printer having a head drive circuit that can generate a less distorted drive waveform stably using a smaller-size and smaller-capacitance transistor than the conventional.
In order to achieve the above objects, an inkjet printer of one aspect of the present invention comprises a head which includes a plurality of piezoelectric elements and may jet ink using the piezoelectric elements, a carriage which has the head and moves with the head, and a one-chip head drive circuit, provided in the carriage, which receives a control signal and a drive signal for driving the piezoelectric elements, and drives the head, wherein the head drive circuit includes a plurality of selection parts, connected to each of the piezoelectric elements, which may receive the drive signal, a control part, coupled to the selection parts, which controls the selection parts based on the control signal, and selects a piezoelectric element to be driven from among the piezoelectric elements, and a plurality of current amplifier parts, provided in every selection part and piezoelectric element, which amplify the drive signal to be supplied to the piezoelectric element to be driven.
An inkjet printer of another aspect of the present invention comprises a head which includes a plurality of piezoelectric elements and may jet ink using the piezoelectric elements, and a head drive circuit that receives a control signal and those plural types of drive signals which drive the piezoelectric elements, and drives the head, wherein the head drive circuit includes a plurality of selection parts, connected to each of the piezoelectric elements, which may receive each of the plural types of drive signals, a control part, coupled to the selection parts, which controls the selection parts based on the control signal, and selects a piezoelectric element to be driven from among the piezoelectric elements and a drive signal to be used from among the drive signals, and a plurality of current amplifier parts, provided in every selection part and piezoelectric element, which amplify the drive signal to be supplied to the piezoelectric element to be driven. Such an inkjet printer is suitable for multi-gradation and/or color inkjet printers.
A head drive circuit of the present invention that receives a control signal and those plural types of drive signals for driving piezoelectric elements and which drives the piezoelectric elements in a head, the head including the plurality of piezoelectric elements and being able to jet ink using the piezoelectric elements, comprises a plurality of selection parts, connected to each of the piezoelectric elements, which may receive each of the plural types of drive signals, a control part, coupled to the selection parts, which controls the selection parts based on the control signal, and selects a piezoelectric element to be driven from among the piezoelectric elements and a drive signal to be used from among the drive signals, and a plurality of current amplifier parts, provided in every selection part and piezoelectric element, which amplify said drive signal to be supplied to said piezoelectric element to be driven.
A one-chip head drive circuit of one aspect of the present invention that receives a control signal and a drive signal for driving piezoelectric elements in a head and which drives the piezoelectric elements, the head including the plurality of piezoelectric elements and being able to jet ink using the piezoelectric elements, comprises a plurality of selection parts, connected to each of the piezoelectric elements, which may receive each of the drive signals, a control part, coupled to the selection parts, which controls the selection parts based on the control signal, and selects a piezoelectric element to be driven from among the piezoelectric elements, and a plurality of current amplifier parts, provided in every selection part and piezoelectric element, which amplify the drive signal to be supplied to the piezoelectric element to be driven.
The inkjet printers and head drive circuits of the present invention require no bulk-sized transistors seen in the prior art, because each piezoelectric element is equipped with one current amplifier part in the head drive circuit. In addition, the head drive circuit may include a voltage amplifier part that is commonly connected to each current amplifier part, thereby reducing the number of voltage amplifier parts in comparison with current amplifier parts each having a voltage amplifier part.
Other objects and further features of the present invention will become readily apparent from the following description of the embodiments with reference to accompanying drawings.